1. Field of the Invention
The present invention concerns a method and a device for protecting against overloads an electrical converter circuit fed with a pulsed current from a primary source.
It applies in particular, but not exclusively, to converter circuits such as voltage regulated power supplies which must be kept within acceptable operating limits for their components and which must be adapted to dissipate the maximum possible losses without overheating.
2. Description of the Prior Art
The protection devices usually employed for this purpose operate on the converter circuit to limit its output power when the latter (or the power supplied by the source) reaches a predetermined threshold. These devices conventionally comprise means for calculating this power and means for comparing it with a threshold value. Further means are provided for transmitting to the converter a signal causing said limitation to be applied when the output power reaches said threshold.
If the converter has only one regulated voltage output the power is monitored by measuring the current supplied.
This basic principle can be applied only if the voltage regulation is sufficiently accurate.
It cannot be applied to a multiple output converter in which some outputs are not regulated and are subject to significant fluctuations.
The same applies if the total power to be controlled is less than the sum of the maximum powers that can be delivered by each output, which is the case with many commercially available power supplies.
In these various cases in which information relating to the output power cannot be obtained by simple measurement it is necessary to use a calculator circuit whose cost increases steeply with the required accuracy.
This is because to calculate a power P=U.times.I usually entails the use of a costly multiplier which determines a voltage x current product.
Inaccuracy in the calculation of this power results in a corresponding inaccuracy in the operation of the protection circuit which implies overrating the converter and therefore an increase in its cost, if the requirement is to remain within the limiting operating conditions previously referred to.
A particular object of the invention is to eliminate these drawbacks through a solution which makes it possible to reduce the cost of the protection circuit without compromising its accuracy and therefore without requiring the converter to be overrated.